1. Field of the Invention
The present invention relates to an ultrasound imaging system and method for providing adaptive clutter filtering.
2. Description of the Related Art
An ultrasound imaging device detects and displays distribution of blood flow by irradiating an ultrasound wave onto a human body and measuring the Doppler shift frequency of the ultrasound wave reflected from the blood flow.
Even when the irradiated ultrasound wave is focused and concentrated on the blood flow, a portion of the ultrasound wave is propagated in an undesired direction. As a result, a signal reflected from the blood flow and an undesired signal reflected from elsewhere besides the blood flow are mixed together. In this instance, the signal reflected from the blood flow is referred to as a Doppler signal, and the undesired signal reflected from other tissues is referred to as a clutter signal.
In general, when focusing is performed with an ultrasound wave, most energy is propagated to a focal point, and a portion of the ultrasound wave is leaked to an outside of the focal point. However, although a minute ultrasound wave is generally leaked because the reflectivity of blood flow is significantly smaller than a reflected ultrasound wave of peripheral tissues (blood vessel walls, muscles and the like), an amplitude of a clutter signal almost exceeds an amplitude of a Doppler signal from the blood flow.
Accordingly, many clutter filtering methods exist for conventional ultrasonic systems to effectively remove clutter signals when a color Doppler mode is implemented.
The clutter filtering methods include a method using an infinite impulse response (IIR)-type high-pass filter in which cutoff characteristics are predetermined, an adaptive filtering method for selecting an optical cutoff according to signal characteristics of each pixel, a method for removing clutter signals by decomposing elements of an ensemble data per pixel, and the like.
However, the variance, mean frequency, and power of a signal before the application of clutter filtering are used in most of the clutter filtering methods, or the variance, mean frequency, and power of a decomposed signal are used in most of the clutter filtering methods.
In the present invention, implementation of a decision logic of a clutter filter of converting an in-phase/quadrature-phase (I/Q) signal into a frequency domain signal is performed, and then removal of clutter elements according to the clutter elements signal characteristics is performed.